This invention relates to polymers containing guanidino groups which are capable of specifically binding to phosphate.
Kidney disorders are extremely common and may, if treatment is inappropriate or delayed, progress through to end stage renal conditions, the patient subsequently requiring dialysis treatment. Kidney dialysis patients suffer from elevated serum levels of phosphate. In addition, patients who possess inefficient Kidneys frequently develop "kidney stones" consisting of the two extremely insoluble salts, calcium phosphate and calcium oxalate. Both of these anions induce severe toxic effects in such patients. The development of elevated phosphate levels is minimised in these patients by the addition of aluminium hydroxide, magnesium hydroxide or calcium hydroxide or mixtures of any of these compounds in the diet. However the use of magnesium or calcium hydroxide can lead to acute side effects, hence aluminium hydroxide is the compound which is more commonly used. The presence of aluminium ions in the patient's intestine reduces the uptake of phosphate from the diet, thus decreasing the concentration of phosphate in the lumen. The result is a concentration gradient of phosphate from a high level in the blood to a low level in the lumen. Phosphate thus moves out of the blood down this concentration gradient and into the lumen. The continued treatment with aluminium hydroxide or related preparations leads to the gradual accumulation of aluminium ions in body tissues which then have to be removed by the administration of the compound desferrioxamine. Desferrioxamine, an iron-chelator, is known to have side effects, especially in people who are not "iron-overloaded" (for example as a result of blood transfusions). Kidney patients are not iron-overloaded, hence constant use of the compound desferrioxamine to reduce aluminium levels may lead to undesirable side effects.